The dispute is between Sen. Tom Coburn, R-Okla., and Grover Norquist of Americans for Tax Reform. Norquist insists – and many Republican politicans have agreed – that policy makers sign a “no new taxes” pledge. But Norquist’s definition of taxes is broad. For instance, he says eliminating the multi-billion dollar subsidy for ethanol is a tax increase, something Coburn has publicly said is absurb, especially if Republicans are going to be effective in cutting the federal deficit.

There was a complicated procedural vote in the Senate in which 43 Republicans sided with Coburn and against Norquist. (Check out Ezra Klein’s post on the subject if you want to go deeper into the weeds). The practical upshot is Coburn took a big chink out of Norquists’s armor.

Speaking later Tuesday on ”The Last Word with Lawrence O’Donnell” on MSNBC, Coburn said: “Grover’s old news, it doesn’t matter what he says.”